NOx reduction system and method

ABSTRACT

A system for reduction of noxious oxides from an exhaust of an internal combustion engine. The internal combustion engine includes an engine exhaust. A NOx catalytic reactor has at least one inlet in communication with the engine exhaust. A reductant catalytic reactor includes an inlet in communication with a reductant fuel supply, and an outlet in communication with at least one inlet to the NOx catalytic reactor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a system and method for reducing noxious oxides from an exhaust gas of an internal combustion engine, and, more particularly, to such a system and method using a catalytic process.

2. Description of the Related Art

Noxious oxides (NOx) has been the subject of air pollution regulations and control efforts for over 30 years. These efforts began in southern California, but under the direction of the U.S. Environmental Protection Agency (EPA), NOx control efforts are spreading throughout the U.S. and to many major cities worldwide. Increasingly stringent control efforts continue to be mandated by regulatory bodies, both domestically and internationally. In southern California and other areas of the U.S. (representing over 60% of the population) that have not attained EPA's ambient air quality standards, an active trading market exists for NOx “credits”, which have economic value and can be created when controls are installed whose performance exceeds regulatory requirements.

Emission standards in the U.S. will require reduction of diesel emissions for transportation vehicles (light and heavy-duty diesel powered trucks and buses) by as much as 90% from current levels in the 2005-2010 time frame. In addition, emissions levels for boilers-electric generators (especially coal fired boilers) and internal combustion (IC) engine (gas and diesel) powered electric generators are required to meet even more stringent NOx emissions levels. Achieving these levels with acceptable costs and durability will be very difficult for these industries.

NOx reduction approaches presently being developed may present problems and difficulties. Catalyst poisoning, thermal cycling and supplying a practical reductant make the performance and life of NOx adsorbers and lean NOx catalysts problematic. Selective Catalytic Reduction (SCR) requires an external fluid be distributed and carried on commercial vehicles. Combustion control technologies such as Exhaust Gas Recirculation, high injection pressures, variable geometry turbines for air handing and other similar mechanisms used to control NOx emissions from diesel engines add complexity and cost.

What is needed in the art is a NOx reduction system and method which is simpler and does not require an additional fluid (reductant) source on board moving vehicles.

SUMMARY OF THE INVENTION

The present invention provides a system for reduction of noxious oxides including an additional reductant catalytic reactor providing a catalyzed reductant fuel to a NOx catalytic reactor.

The invention comprises, in one form thereof, a system for reduction of noxious oxides from an exhaust of an internal combustion engine. The internal combustion engine includes an engine exhaust. A NOx catalytic reactor has at least one inlet in communication with the engine exhaust. A reductant catalytic reactor includes an inlet in communication with a reductant fuel supply, and an outlet in communication with at least one inlet to the NOx catalytic reactor.

An advantage of the present invention is that a higher NOx reduction is effected (based on the chemical stability/sulfur resistance of the catalyst used) in the exhaust from a diesel engine burning high sulfur diesel fuel.

Another advantage is that one liquid can be used for fuel and to catalytically generate the NOx reductant.

Yet another advantage is that the system is thermally and chemically stable.

Still another advantage is that the system uses only about 3% of the system total fuel for NOx reduction.

A further advantage is that the NOx catalyst, constituting the bulk of the system's catalysts, does not use precious metal catalysts.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic view of an embodiment of the NOx reduction system of the present invention; and

FIG. 2 is graphical representation of NOx reduction which may be achieved using the NOx reduction system shown in FIG. 1.

Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, and more particularly to FIG. 1, there is shown an embodiment of a system 10 for reduction of NOx from an exhaust 12 of an internal combustion engine 14. System 10 also generally includes a NOx catalytic reactor 16, reductant fuel supply 18 and reductant catalytic reactor 20.

Reductant fuel supply 18 contains diesel fuel, gasoline and/or one or more other hydrocarbons. In one embodiment, reductant fuel supply 18 is the same fuel tank which supplies fuel to IC engine 14, and thus reductant fuel 22 within reductant fuel supply 18 is also the same as the fuel supplied to IC engine 14 (e.g., diesel fuel). Configured as such, it will be appreciated that a separate supply line leads from reductant fuel supply 18 to IC engine 14. Although the present invention is described and shown herein with reference to a diesel engine, it should be understood that the present invention is applicable to any hydrocarbon combustion source (e.g., diesel, natural gas, gasoline, coal, alcohols, etc.).

NOx catalytic reactor 16 has an inlet 24 in communication with engine exhaust 12, and an outlet 26 in communication with the ambient environment, and optionally in communication with analyzers for determining a NOx level within the exhaust.

In one embodiment, NOx catalytic reactor 16 includes a ceramic catalyst material comprised of Al₂O₃, doped with (either integrated into the crystal structure of the Al₂O₃ or impregnated with) with an alkaline earth element (Na, Li, K or CS), Zr, Ti, V, Ce or La. In another embodiment, NOx catalytic reactor 16 includes a ceramic catalyst material comprised of Y zeolites, doped with (either integrated into the crystal structure of the zeolite or impregnated with) an alkaline earth element (Na, Li, K, or CS), Zr, Ti, V or La or Beta zeolites doped with Fe.

Reductant catalytic reactor 20 includes an inlet 28 in fluid communication with reductant fuel supply 18, and an outlet 30 in communication with inlet 24 to NOx catalytic reactor 16. More particularly, outlet 30 is coupled with branch exhaust 32 upstream from inlet 24 to NOx catalytic reactor 16. Gases transported from outlet 30 of reductant catalytic reactor 20 therefore mix with engine exhaust gases from exhaust 12, prior to entering NOx catalytic reactor 16 at inlet 24.

Pump 34 and coil heater 36 are disposed in a series arrangement between reductant fuel supply 18 and reductant catalytic reactor 20. Regulator 38 controls the volumetric fluid flow through pump 34, and ultimately to reductant catalytic reactor 20. Heater 36 heats the reductant fuel outputted from pump 34 to a temperature of between approximately 450-600° F., which is necessary to maintain a minimum temperature required to drive the reforming/cracking process of the reductant fuel within reductant catalytic reactor 20.

Reductant catalytic reactor 20 includes a cracking and/or reforming catalyst used for reductant formation. In one embodiment, the cracking and/or reforming catalyst is comprised of zeolites, silica aluminas, precious metals wash coated on Al203 wash coated onto extruded corrigated monolith cylinders and/or Al₂O₃ or a combination of these compounds (needed to produce the desired combination of reductants to optimize NOx reduction at a given exhaust condition). The zeolites are preferably of ZSM5 configuration with a SiO2 to Al2O3 ratio of from 5-1000. These zeolites may be used in the pure form or doped with (impregnated or integrated into the crystal structure) Mo, Ti, Fe. The Silica Aluminas are solid solutions of SiO2 and Al2O3 oxides that are doped with Mo, Ti, and/or Fe.

During use, diesel fuel, gasoline or other hydrocarbons are catalytically cracked and/or reformed to produce H₂, CO and/or short chain hydrocarbons (oxidized and partially unsaturated) to act as reductants for NOx when passed over NOx catalytic reactor 16 in conjunction with the NOx from exhaust 12 originating from IC engine 14. The cracked and/or reformed reductant fuel is mixed with the engine exhaust in branch exhaust 32 and transported to inlet 24 of NOx catalytic reactor 16. The equation for the reductant reaction in NOx catalytic reactor 16 is:

HC, CO and/or H₂ (one or all)+NOx=>N₂+CO₂+H₂0 (dependent upon the reductant mix).

Unlike three-way catalysts used on automobiles for NOx reduction, system 10 reduces NOx in the presence of high concentrations of O₂ (less than 1%) and sulfur oxides (less than 15 ppm) normally found in the exhaust of diesel and lean burn natural gas/gasoline engine powered vehicles as well as most coal and natural gas fired boilers.

System 10 uses a unique cracking/reforming catalyst to produce a tailored, very active reductant to activate a normally very thermally and chemically inactive ceramic catalyst to reduce NOx in the presence of high levels of sulfur oxide and oxygen. This unique combination of catalysts produces a NOx reduction after treatment system that is very sulfur tolerant and thermally stable and cost effective since the NOx catalyst (constituting the bulk of the system catalyst) does not use precious metals and is very efficient since it only involves a 2-3 fuel penalty. System 10 has demonstrated over 90% NOx reduction (FIG. 2) in the exhaust from an IC engine 14 burning high sulfur (500 ppm) diesel fuel.

In contrast with conventional systems, the present invention catalytically and thermally produces, under controlled conditions, taylored reductants from commercially available hydrocarbons (such as diesel fuel and gasoline) that will cause materials that are not normally able to (or catalytically active for) effectively reduce the oxides of nitrogen from the exhausts of combustion sources. These normally inactive materials are preferably ceramics and are very stable thermally and chemically (are not poisoned by active compounds in the exhaust such as SOx) giving these materials the double benefit of being both very active for NOx but very stable thermally and chemically otherwise.

While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims. 

1. A system for reduction of noxious oxides from an exhaust of an internal combustion engine, comprising; an internal combustion engine including an engine exhaust; a NOx catalytic reactor having at least one inlet in communication with said engine exhaust; a reductant fuel supply; a reductant catalytic reactor including an inlet in communication with said reductant fuel supply and an outlet in communication with said at least one inlet to said NOx catalytic reactor, said reductant catalytic reactor not directly connected to the atmosphere and operating without ambient air being introduced directly thereto: a heater in communication with said reductant catalytic reactor inlet whereby said fuel supply is heated prior to entering the reductant catalytic reactor, and, wherein said reductant catalytic reactor comprises one of a zeolites and precious metals.
 2. The system for reduction of noxious oxides of claim 1, further including a pump in communication with and between said reductant fuel supply and said reductant catalytic reactor.
 3. The system for reduction of noxious oxides of claim 2, further including a regulator for controlling fluid flow through said pump.
 4. The system for reduction of noxious oxides of claim 2, wherein said heater is in communication with and between said pump and said reductant catalytic reactor.
 5. The system for reduction of noxious oxides of claim 4, wherein said heater heats reductant fuel from said reductant fuel supply to a temperature of between approximately 450 to 600 degF.
 6. A system for reduction of noxious oxides from an exhaust of an internal combustion engine, comprising; an internal combustion engine including an engine exhaust; a NOx catalytic reactor having at least one inlet in communication with said engine exhaust; a reductant fuel supply; a reductant catalytic reactor including an inlet in communication with said reductant fuel supply and an outlet in communication with said at least one inlet to said NOx catalytic reactor, said reductant catalytic reactor not directly connected to the atmosphere and operating without ambient air being introduced directly thereto; a heater in communication with said reductant catalytic reactor inlet whereby said fuel supply is heated prior to entering the reductant catalytic reactor, and, wherein said NOx catalytic reactor includes a ceramic catalyst material comprised of Al₂0₃, doped with one of Na, Zr and La.
 7. A system for reduction of noxious oxides from an exhaust of an internal combustion engine, comprising; an internal combustion engine including an engine exhaust; a NOx catalytic reactor having at least one inlet in communication with said engine exhaust; a reductant fuel supply; a reductant catalytic reactor including an inlet in communication with said reductant fuel supply and an outlet in communication with said at least one inlet to said NOx catalytic reactor, said reductant catalytic reactor not directly connected to the atmosphere and operating without ambient air being introduced directly thereto; a heater in communication with said reductant catalytic reactor inlet whereby said fuel supply is heated prior to entering the reductant catalytic reactor, and, wherein said NOx catalytic reactor includes a ceramic catalyst material comprised of Y zeolite, doped with Na.
 8. (canceled)
 9. The system for reduction of noxious oxides of claim 1, wherein said reductant catalytic reactor is doped with at least one of Mo, Ti and Fe.
 10. The system for reduction of noxious oxides of claim 9, wherein said reductant fuel supply can be any one of diesel fuel, gasoline and one or more other hydrocarbons.
 11. The system for reduction of noxious oxides of claim 9, wherein said internal combustion engine utilizes fuel in the form of at least one of diesel, natural gas, gasoline, coal, and alcohol.
 12. A system for reduction of noxious oxides from an exhaust of an internal combustion engine, comprising; a NOx catalytic reactor having at least one inlet configured for communication with said engine exhaust; a reductant fuel supply; a reductant catalytic reactor including an inlet in communication with said reductant fuel supply and an outlet in communication with said at least one inlet to said NOx catalytic reactor, said reductant catalytic reactor not directly connected to the atmosphere and operating without ambient air being introduced directly thereto; a heater in communication with said reductant catalytic reactor inlet whereby said fuel supply is heated prior to entering the reductant catalytic reactor; and, said reductant catalytic reactor operating with said fuel supply in the absence of water being provided thereto.
 13. The system for reduction of noxious oxides of claim 12, further including a pump in communication with and between said reductant fuel supply and said reductant catalytic reactor.
 14. The system for reduction of noxious oxides of claim 13, further including a regulator for controlling fluid flow through said pump.
 15. The system for reduction of noxious oxides of claim 13, wherein said heater is in communication with and between said pump and said reductant catalytic reactor.
 16. The system for reduction of noxious oxides of claim 12, wherein said reductant catalytic reactor includes at least one of zeolites, silica aluminas, dispersed precious metals on monolith, and aluminum trioxide.
 17. The system for reduction of noxious oxides of claim 16, wherein said reductant catalytic reactor is doped with at least one of these metals Mo, Ti and Fe.
 18. A method of reducing noxious oxides from an exhaust of an internal combustion engine, comprising the steps of: heating a reductant fuel; at least one of cracking and reforming a said reductant fuel in the absence of ambient air in a reductant catalytic reactor comprising one of a zeolites and precious metals; mixing the at least one of cracked and reformed reductant fuel with exhaust gas from the internal combustion engine; and catalytically converting the mixed reductant fuel and exhaust gas in a NOx catalytic reactor.
 19. The method of reducing noxious oxides of claim 18, wherein said reductant fuel comprises any one of diesel fuel, gasoline and one or more other hydrocarbons prior to being at least one of cracked and reformed.
 20. (canceled)
 21. The method of reducing noxious oxides of claim 18, wherein said reductant catalytic reactor is doped with at least one of Mo, Ti and Fe. 